Particle blast cleaning apparatuses using sublimable media are well known in the industry. U.S. Pat. No. 4,947,592, which is incorporated herein by reference, describes in detail a particle blast cleaning apparatus in which carbon dioxide pellets are formed and introduced into a flow of high pressure transport gas. The carbon dioxide pellets are carried, entrained in the transport gas, through a hose having a discharge nozzle at its exit end. The flow of the entrained carbon dioxide pellets is directed by the nozzle at a particular work piece so as to perform some function thereon, such as cleaning, coating removal or deflashing, for example.
Frequently, it is desirable to have more than one nozzle available for use in a situation where the multiple nozzles will not be used simultaneously. Because of the high cost of the equipment necessary to create the carbon dioxide pellets and transport them entrained in the transport gas for discharge through a nozzle, it is desirable to connect multiple nozzles and associated hoses to a single source of carbon dioxide pellets.
Because the temperature of the flow is in the range of minus 60.degree. F. to minus 110.degree. F., and because the pressure of the transport gas is typically very high, ranging up to 350 psig, it is difficult for a flow diverter valve to operate reliably. Because of the cryogenic temperatures, any moisture which reaches any components of the flow diverter valve may form water ice which can build up and interfere with the proper operation of the flow diverter valve. Sources of such moisture include the ambient air surrounding the flow diverter valve, and to a lesser extent the high pressure transport gas. Sealing against leakage of the transport gas at moveable joints, as are present in a flow diverter valve, is particularly difficult because of the high pressures involved and the contraction of the components caused by the cold temperatures. The problem is exacerbated by the fact that the joints which are susceptible to leakage are typically located in areas of the flow diverter valve which are very susceptible to being blocked by any water ice build up, thereby preventing proper operation.
Additionally, the flow of the carbon dioxide pellets entrained in the high pressure transport gas is particularly susceptible to agglomeration. The flow diverter valve must not interfere with the flow or cause agglomeration. The valve must have a negligible pressure drop through it, and present very little disturbance to the laminar flow of pellets within the flow stream.